Field of the Invention
The present invention relates to a focus detection apparatus for performing a focus detection on the basis of a phase difference between pupil-divided images obtained by using an image pickup element in which a plurality of photoelectric conversion units are provided for one microlens and, more particularly, to a signal processing apparatus for performing a focus detection which is not affected by a perspective conflict.
Description of the Related Art
In recent years, such a technique that pupil-separated images are obtained by an image pickup element in which a plurality of photoelectric conversion units are arranged for one microlens, and a focus detection is performed on the basis of a phase difference between the obtained two pupil-divided images has been known.
For example, the Official Gazette of Japanese Patent Application Laid-Open No. 2001-083407 (Patent Literature 1) discloses such a technique that a phase difference is obtained by pupil-separated images to perform a focus detection, and at the same time, all pixels corresponding to a same microlens are added to be handled as one pixel. By adding all of the pixels corresponding to one microlens, they are handled in substantially the same manner as that of a pixel array of an image pickup apparatus in the related art, thereby enabling an image for appreciation to be formed by a signal processing technique in the related art.
The Official Gazette of Japanese Patent No. 4591120 (Patent Literature 2) discloses such a technique that in a contrast AF, when there is a perspective conflict, a portion where a focusing position is already known is masked, thereby detecting another object.
However, according to the related art disclosed in foregoing Patent Literature 2, an attention is paid to an evaluation value of the contrast AF and such a technique cannot be applied, as it is, to a focus detection method using the phase difference of Patent Literature 1.
In a phase difference method which is put into practical use in a single lens reflex camera, the existence of a plurality of focusing positions at the time of a perspective conflict can be discriminated on the basis of ups and downs of a correlation image waveform at the time of a correlation operation.
However, in the case of pupil-dividing an object at an image pickup element plane as shown in Patent Literature 1, it is difficult to recognize the existence of a plurality of focusing positions by the ups and downs of the correlation image waveform.
This is because although a sensor for detecting a phase difference of a single lens reflex camera uses pupil-divided images of a deep depth of field, since the technique of Patent Literature 1 uses the pupil-divided images of a depth of field of the image for appreciation, that technique is largely affected by a focusing state at the time when an image for distance measurement is obtained. It is, therefore, difficult to grasp a perspective conflict state by using the technique of Patent Literature 1.